soap is bad for crabs.... Which is why when you clean the tank initially before putting anything in you do not use soap. And I would imagine pepper could be bad if it's mixed in substrate. I believe they can eat fresh pepper. but mixed in it might get in their eyes or in their shell and irritate them.

Just lmake sure when you get the new sand that there isn't a "diesel-like" smell to it and if there is go somewhere else to do your business because sands contaminated with certain chemicals can harm crabs.